Polyaromatic hydrocarbons (PAHs) are significant pollutants at Superfund sites. They are often toxic and may be carcinogenic. Consequently, research is needed on practical methods to remove the PAHs from contaminated groundwaters. PAHs are usually accompanied at these sites by heavy metals such as arsenic and cadmium. Unfortunately, little is known about the interactions between PAHs and heavy metals and the effect the presence of these metals may have on PAH bioremediation. Complex mixtures of toxic organics and metals are difficult to study and have, therefore, been largely ignored. The overall goal of this research s to gain an understanding of the transport and biodegradation mechanisms of complex mixtures of toxic pollutants at Superfund sites. We will be studying a novel groundwater treatment systems known as a "biowall" or permeable bio-barrier system. Determining the role of biofilm in permeable bio-barrier systems is crucial to the design of more efficient treatment systems since the mass transport mechanisms, structural forms, and biodegradation processes in soil biofilms are not well understood. The engineering component will focus on design and evaluation of mulch-based biowalls and development of pollutant monitoring microelectrodes for application in studying the biodegradation of PAH-metal mixtures in water aquifers at Superfund sites. The potential use of fungi in the biowall will be examined. Research will be conducted in a simulated Superfund testbed that replicates a contaminated groundwater system. The successful monitoring of biofilms and pore water at Superfund sites will also improve process efficiency in bioremediation treatment. Therefore, microelectrodes developed in previous SBRP research will be modified for field use and tested in the testbeds.. In addition, a new MEMS-based heavy metal analyzer for use in the field will be developed. The result of this research-will be a better understanding of how complex mixtures of toxic materials can be bioremediated at Superfund sites so as to reduce the potential impact of these PAHs and heavy metals on human health.